If you did as Chienworks stated then place your green screen video of yourself on track one and your background video on track 2. Click the event fx box for the green screen video and apply the chroma key filter. Use the dropper to select the green (or whatever color) background you have and the green will disappear and leave you superimposed over your background video on track 2. There are adjustments you can make to fine tine the key.

Hi Chienworks, no I didn't record in front of a green screen or a solid colour background, as I didn't know that I had to.

Obviously that's what I should have done, so if I get a piece of green cloth, held in position, firstly will that be good enough and secondly what do i then do to make it look as if I'm actually there in the picture (so to speak)?

By the way dos the green cloth have to be shiny, flat, dark or light?

Thanks

Hypnoman

Flat, not shiny, and mid-toned is far better than light or dark. Green also isn't important. It just has to be some color that doesn't appear in the subject (you). If you're wearing a green shirt then you might be better off chosing purple for the background.

The background has to be evenly lit so that it isn't lighter in one corner and darker on the opposite side. A small amount of variation is ok, but less variation will work better and easier. Light it from the sides or behind you so that you don't cast a shadow on it.

Once you've shot yourself in front of this cloth follow Terry's instructions.